Bandgap reference circuit with tunable current source

Abstract

A bandgap reference circuit includes a voltage reference circuit configured to generate a reference voltage at a first output and a proportional to absolute temperature (PTAT) current source configured to generate a PTAT current reference at a second output. A divider circuit is coupled to the reference voltage and configured to generate a divided reference voltage at a third output of the bandgap reference circuit. The bandgap reference circuit further includes a tunable current source coupled to the divider circuit and configured to generate a tunable current reference at a fourth output of the bandgap reference circuit based, at least in part, on the divider circuit. A method of generating a tunable current with a bandgap circuit is also provided.

What is claimed is: 
     
       1. A bandgap reference circuit, comprising:
 a voltage reference circuit comprising a first transistor having a first junction voltage and a second transistor having a second junction voltage, wherein the voltage reference circuit is configured to generate a reference voltage at a common control node coupled to the first and second transistors, the reference voltage based, at least in part, on a voltage difference between the first junction voltage and the second junction voltage, wherein the reference voltage is provided at a first output of the bandgap reference circuit; 
 a proportional to absolute temperature (PTAT) current source configured to generate a PTAT current reference at a second output of the bandgap reference circuit based, at least in part, on a current through the first transistor; 
 a divider circuit connected to the common control node and configured to generate a divided reference voltage having a voltage value that is a fraction of a voltage value of the reference voltage, wherein the divided reference voltage is provided at a third output of the bandgap reference circuit; 
 a tunable current source coupled to the divider circuit and configured to generate a tunable current reference at a fourth output of the bandgap reference circuit based, at least in part, on the divider circuit; and 
 an amplifier stage having a first input coupled to the first transistor, a second input coupled to the common control node, and an output coupled to a common drain stage, wherein the tunable current source is coupled to a first terminal of the common drain stage and the divider circuit is coupled to a second terminal of the common drain stage at which the reference voltage is provided. 
 
     
     
       2. The bandgap reference circuit of  claim 1 , wherein the divider circuit comprises a resistor ladder coupled between the first output of the bandgap reference circuit and a reference potential and having an intermediate node at which the divided reference voltage is provided. 
     
     
       3. The bandgap reference circuit of  claim 2 , wherein the divider circuit further comprises at least one resistor coupled in parallel with the resistor ladder. 
     
     
       4. The bandgap reference circuit of  claim 3 , wherein the resistor ladder comprises at least two resistors having a temperature coefficient of a first polarity and wherein the at least one parallel-coupled resistor has a temperature coefficient of a second polarity. 
     
     
       5. The bandgap reference circuit of  claim 4 , wherein one of the at least two resistors of the resistor ladder or the at least one parallel-coupled resistor comprises an n-type resistor, and the other one of the at least two resistors of the resistor ladder and the at least one parallel-coupled resistor comprises a p-type resistor. 
     
     
       6. The bandgap reference circuit of  claim 4 , wherein at least one of the at least two resistors of the resistor ladder and the at least one parallel-coupled resistor includes a variable resistor, and wherein a current level of the tunable current reference is tunable by selection of a resistance associated with the variable resistor. 
     
     
       7. The bandgap reference circuit of  claim 3 , wherein a current level of the tunable current reference is tunable by selection of a resistance associated with the resistor ladder and a resistance associated with the at least one parallel-coupled resistor, and wherein a temperature coefficient of the tunable current reference is tunable by adjusting a ratio of the resistance associated with the resistor ladder with respect to the resistance associated with the at least one parallel-coupled resistor. 
     
     
       8. The bandgap reference circuit of  claim 7 , wherein the current level of the tunable current reference is substantially flat over temperature and a supply voltage. 
     
     
       9. The bandgap reference circuit of  claim 1 , wherein the common drain stage comprises a field effect transistor (FET). 
     
     
       10. A method of generating a tunable current with a bandgap circuit, comprising:
 providing a bandgap reference voltage; 
 dividing the bandgap reference voltage with a resistor ladder comprising at least two resistors of a first resistor type; 
 coupling at least one resistor in parallel with the resistor ladder, wherein the at least one parallel-coupled resistor is of a second resistor type, different than the first resistor type; 
 providing a current reference; and 
 tuning a current level of the current reference to be substantially flat over temperature and a supply voltage by selection of a resistance associated with the resistor ladder and a resistance associated with the at least one parallel-coupled resistor, and tuning a temperature coefficient of the current reference by adjusting a ratio of the resistance associated with the resistor ladder with respect to the resistance associated with the at least one parallel-coupled resistor. 
 
     
     
       11. The method of  claim 10 , wherein dividing the bandgap reference voltage with a resistor ladder comprising at least two resistors of a first resistor type comprises dividing the bandgap reference voltage with a resistor ladder comprising at least two resistors having a temperature coefficient of a first polarity. 
     
     
       12. The method of  claim 11 , wherein coupling at least one resistor in parallel with the resistor ladder comprises coupling at least one resistor having a temperature coefficient of a second polarity in parallel with the resistor ladder. 
     
     
       13. The method of  claim 10 , wherein one of the at least two resistors of the resistor ladder or the at least one parallel-coupled resistor comprises an n-type resistor, and the other one of the at least two resistors of the resistor ladder and the at least one parallel-coupled resistor comprises a p-type resistor. 
     
     
       14. A bandgap reference circuit, comprising:
 a voltage reference circuit comprising a first transistor having a first junction voltage and a second transistor having a second junction voltage, wherein the voltage reference circuit is configured to generate a reference voltage at a common control node coupled to the first and second transistors, the reference voltage based, at least in part, on a voltage difference between the first junction voltage and the second junction voltage, wherein the reference voltage is provided at a first output of the bandgap reference circuit; 
 a proportional to absolute temperature (PTAT) current source configured to generate a PTAT current reference at a second output of the bandgap reference circuit based, at least in part, on a current through the first transistor; 
 a divider circuit coupled to the reference voltage and configured to generate a divided reference voltage having a voltage value that is a fraction of a voltage value of the reference voltage, wherein the divided reference voltage is provided at a third output of the bandgap reference circuit; and 
 a tunable current source coupled to the divider circuit and configured to generate a tunable current reference at a fourth output of the bandgap reference circuit based, at least in part, on the divider circuit, wherein the current level of the tunable current reference is substantially flat over temperature and a supply voltage. 
 
     
     
       15. The bandgap reference circuit of  claim 14 , further comprising an amplifier stage having a first input coupled to the first transistor, a second input coupled to the common control node, and an output coupled to a common drain stage, wherein the tunable current source is coupled to a first terminal of the common drain stage and the divider circuit is coupled to a second terminal of the common drain stage at which the reference voltage is provided. 
     
     
       16. The bandgap reference circuit of  claim 15 , wherein the divider circuit comprises a resistor ladder coupled between the first output of the bandgap reference circuit and a reference potential and having an intermediate node at which the divided reference voltage is provided. 
     
     
       17. The bandgap reference circuit of  claim 16 , wherein the divider circuit further comprises at least one resistor coupled in parallel with the resistor ladder and wherein the resistor ladder comprises at least two resistors having a temperature coefficient of a first polarity and wherein the at least one parallel-coupled resistor has a temperature coefficient of a second polarity. 
     
     
       18. The bandgap reference circuit of  claim 17 , wherein a current level of the tunable current reference is tunable by selection of a resistance associated with the resistor ladder and a resistance associated with the at least one parallel-coupled resistor, and wherein a temperature coefficient of the tunable current reference is tunable by adjusting a ratio of the resistance associated with the resistor ladder with respect to the resistance associated with the at least one parallel-coupled resistor.